The present invention is directed to an optical add/drop multiplexer for use in a dense wavelength division multiplexed optical system.
Optical communication systems are a substantial and fast growing constituent of communication networks. The expression xe2x80x9coptical communication system,xe2x80x9d as used herein, relates to any system that uses optical signals to convey information across an optical waveguiding medium, for example, an optical fiber, and can also refer to transmission through free-space. Such optical systems include but are not limited to telecommunication systems, cable television systems, and local area networks (LANs). Currently, many optical communication systems are configured to carry an optical channel of a single wavelength over one or more optical waveguides. To convey information from plural sources, time-division multiplexing is frequently employed (TDM). In time-division multiplexing, a particular time slot is assigned to each signal source, the complete signal being constructed from the portions of the signals collected from each time slot. While this is a useful technique for carrying plural information sources on a single channel, its capacity is limited by fiber dispersion and the need to generate high peak power pulses.
While the need for communication services increases, the current capacity of existing waveguiding media is limited. Although capacity may be expanded e.g., by laying more fiber optic cables, the cost of such expansion is prohibitive. Consequently, there exists a need for a cost-effective way to increase the capacity of existing optical waveguides.
Wavelength division multiplexing (WDM) has been explored as an approach for increasing the capacity of existing fiber optic networks. WDM systems typically include a plurality of transmitters, each respectively transmitting signals on a designated one of a plurality of channels or wavelengths. In a simple point-to-point network, the channels are combined by a multiplexer at one end terminal and transmitted on a single fiber to a demultiplexer at another end terminal where they are separated and supplied to respective receivers. In more complex systems, an add/drop multiplexer may be present at each node for dropping one or more particular channels from the DWDM signal, and subsequently adding the one or more channels back to the signal prior to transmission to another network node.
In high channel count systems, the add/drop multiplexer can be relatively complex and expensive. In addition, many customers may initially deploy few channels, with the expectation that significantly more channels will be added later on. Accordingly, the add/drop multiplexer is preferably scalable to accommodate additional channels. Moreover, a residual amount of dropped channel power can pass through the add/drop multiplexer and interfere with the added channel light, thereby degrading system performance. Accordingly, there is a need for an add/drop multiplexer that can be arbitrarily configured to add and drop desired channels in a WDM system, and overcomes these problems.
Consistent with the present invention, an optical device is provided comprising an optical splitter having an input for coupling to an input optical path carrying a plurality of optical channels, each the optical channels having a respective wavelength. The splitter includes first and second outputs. The first output is coupled to a first output optical path, and the second output is coupled to a second output optical path. The first and second output optical paths carry the plurality of optical channels.
A first plurality of optical filtering elements is coupled to the first output optical path for respectively selecting first groups of the plurality of optical channels and associated undesired channels. A second plurality of optical filtering elements is coupled to the second output optical path for respectively selecting second groups of the plurality of optical channels and associated undesired channels. The first groups of optical channels are different than the second groups of optical channels.
At least one cleanup filter is coupled to an associated one of the first and second plurality of optical filtering elements for receiving one of the first and second groups of optical channels and the undesired channels associated with the received one of the first and second groups of optical channels. The cleanup filter supplies the associated one of the first and second groups of optical channels as an express channel group while reducing the undesired channels associated with the associated one of the first and second group of optical channels.
A multiplexer receives each of the express channel groups and at least one added channel group on associated inputs. Each of the added channel groups is different from each of the express channel groups. The multiplexer supplies an output comprising the express channel groups and the added channel groups in an aggregated form on a single optical output fiber.
A sub-demultiplexer may be coupled to an associated one of the first and second plurality of optical filtering elements. The sub-demultiplexer may have a plurality of outputs each presenting a respective drop channel associated with a corresponding one of the first and second groups of the plurality of channels. Also, a sub-multiplexer having a plurality of inputs each configured to receive a respective add channel associated with one of the add channel groups may be provided. The sub-multiplexer supplies an output to the multiplexer comprising one of the add channel groups.